Disconnect Switch: Learn the Purpose, Cost, and Lead Time to Procure

Purpose of disconnect switch

Disconnect switches establish isolation points for equipment maintenance. They are installed on both sides of the circuit breaker, high-side of the transformer, and on the line exit.

*Location of disconnect switches inside a substation*

Switches cannot and should not be used to interrupt load current or fault current. A switch operation takes place after the circuit is de-energized.

Disconnect Switch: Learn the Purpose, Cost, and Lead Time to Procure 1 — *Arcing shown here occurs during to capacitive charging current from long lines. When the switch is on a transformer, arcing occurs due to the magnetizing current.*

Cost of disconnect switch

A switch can be designed numerous ways – vertical break, center break, side break, double side break, pantograph, etc. View some of them here. The style you want depends on how the substation bus is laid out. The prices below reflect your typical vertical break configuration.

15kV 600A/1200A disconnect switch with manual operator: ~$7,000
35kV 1200A disconnect switch with manual operator: ~$7,000
69kV 1200A disconnect switch with manual operator: ~$14,000
138kV 2000A disconnect switch with motor operator: ~$20,000
230kV 3000A disconnect switch with motor operator: ~$33,000
345kV 3000A disconnect switch with motor operator: ~$66,000
500kV 3000A disconnect switch with motor operator: ~$102,000
765kV 3000A disconnect switch with motor operator: ~$150,000

Note: The cost includes the price of structural steel. For 138kV and above, the price of steel for high switch stand used (for conservative figures).

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Lead time to procure disconnect switch

~22 weeks for a high voltage switch.

Information on cost and lead time is for your general knowledge only. Contact vendor with your equipment specifications for actual figures.

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Disconnect Switch: Learn the Purpose, Cost, and Lead Time to Procure 2

Substation Major Equipment

It's only stupid-simple, let's begin.

An industrial facility is plagued with voltage flicker (due to harmonics) and poor power factor at the service entrance. Which device would you install to fix both issues?

Voltage regulator

Install capacitor bank

Harmonic filter bank

You are building an interconnect station, tying wind farm generation to the power grid. At the substation, the sources are tied through a tie-breaker. Which device would you install to make sure the sources are synchronized?

Current transformer

Voltage transformer

Ideal transformer

Power transformer

What's the purpose of a conventional power transformer?

Transform power, voltage, and current

Transform voltage and current

Transform voltage only

For which event should a surge arrester operate? Check all that apply.

Phase-to-ground short-circuit

Switching surge

Temporary overvoltage

Lightning strike

Which combination of devices would you use to implement power line carrier?

Wavetrap, capacitor coupled voltage transformer, and line tuner

Wave trap, capacitor voltage transformer and line tuner

Wave trap and line tuner

A transformer develops an internal fault. Which device would you install on the transformer high-side to interrupt fault current?

Disconnect switch

Circuit breaker

Either a breaker or a circuit switcher

Circuit switcher

In a distribution substation, the available ground-fault current on the low side of the step-down transformer is excessive, over-dutying the switching equipment. What is your cost-effective solution to reducing the fault current?

Add current limiting fuses in series on the switchgear

Add series inductors

Add inductor in the transformer neutral

Buy new transformer with higher impedance (%Z)

Your score is

The average score is 45%

3 thoughts on “Disconnect Switch: Learn the Purpose, Cost, and Lead Time to Procure”

pious mahu
March 7, 2022 at 8:00 am

It was very very helpful, thank you very much

Reply
+Doug Willoughby
January 22, 2021 at 11:49 am

I am having strong RFI from a local power company in Mesa, Arizona (SRP) and they think that it may be due to the Disconnect Switches they are using. Is that typical for these products since they operate at very high voltages? I am a Ham Operator and am receiving considerable RFI on the 3.5-7.5 mhz frequency bands. Any suggestions on how I might be able to prevent that from getting into my antenna system? Their Substation is about 1/2 block from my location.

Regards,
Doug Willoughby, K7GJX

Reply
1. Anonymous
  January 22, 2021 at 1:07 pm
  
  Corona discharge from EHV conductors can cause radio interference. What voltage is the substation? Substation design standards require corona mitigation at extra high voltages (345kV and above).
  Corona discharge is absolutely possible during EHV switch operation. But switch operation happens occasionally. So, if it’s a consistent interference then it’s something else.
  
  Reply